Lateral flow type devices for the detection and quantification of an analyte of interest in a fluid sample are well known. For example, such devices are described in U.S. Pat. Nos. 3,799,742; 3,811,840; 3,645,687; 4,435,504; 4,094,647; 3,246,339; 4,366,241; 3,888,629, and 5,750,333, each of which is incorporated by reference herein in its entirety. Generally, the devices comprise a solid phase fluid permeable flow path having immobilized thereon various capture reagents for the analyte (or analogue thereof) or conjugates involving binding partners for the analyte and members of signal producing systems (e.g., a label). The various assay formats used with these devices are well known for the direct or indirect detection of the analyte of interest in the test sample.
Numerous materials are known for the solid phase flow paths of the lateral flow devices. These materials are generally selected to have a low affinity for sample materials and other specific binding reagents, the ability to transport liquid by capillary action over a distance with consistent liquid flow across the flow path, and ready binding to immobilized specific binding reagents. The material chosen for a solid phase flow path partially controls the speed of fluid flow through the flow path. Flow speed is one of the variables that affect the sensitivity of the assay. If the sample flows too fast past the capture reagents immobilized on the flow path, specific binding reactions may not have enough time to occur, thus reducing the sensitivity of the assay. On the other hand, when liquid flows too slowly, the total time to complete the assay increases. This may be undesirable since the speed of the assay is an important feature for the consumer.
Balancing assay sensitivity with assay time provides a challenge since a single material may not provide all of the desired characteristics for the solid phase fluid flow path. Those materials that do provide such characteristics may be difficult and expensive to manufacture. Thus, what is needed is a convenient and cost effective method of balancing the total assay time with the sensitivity of the assay, while allowing easy manufacturability of the device.